Asthma and other respiratory diseases have long been treated by the inhalation of appropriate medicament. For many years the two most widely used and convenient choices of treatment have been the inhalation of medicament from a drug solution or suspension in a metered dose pressurised inhaler (MDI), or inhalation of powdered drug generally admixed with an excipient, from a dry powder inhaler (DPI). With growing concern being voiced over the strong link between depletion of the earth's ozone layer and chlorofluorocarbon (CFC) emissions, the use of these materials in pressurised inhalers is being questioned and interest in DPI systems has been stimulated.
Existing single and multiple dose dry powder inhalers use either individual pre-measured doses or bulk powder reservoirs. In both cases only fairly large quantities (e.g., several hundred micrograms) can constitute a dose due to problems associated with accurately transferring a measured small quantity of powder either into a capsule, or from a bulk reservoir within an inhaler. With potent drugs this introduces the necessity to add excipients, such as lactose powder, to increase the quantity of powder to be measured. These excipients are undesirable, however, as they pose subsequent powder deagglomeration problems and cause dryness in the patient's mouth. In addition, the use of individual pre-measured doses tends to lead to the production of bulky inhalation devices.
Dry powder inhalers in which the medicament is introduced into the device from a capsule are disclosed in U.S. Pat. Nos. 3,948,264, 3,971,377 and 4,147,166 and British Patent No. 1479283. Dry powder inhalers having a reservoir of dry powder from which unit doses are transferred to a chamber by means of a delivery system, such as a rotating perforated membrane in which the perforations are filled with powder from the reservoir, are disclosed in British Patent Application Nos. 2102295 and 2144997 and European Patent Application Nos. 69715, 79478 and 166294.
U.S. Pat. No. 4,735,358, European Patent Application No. 239802 and British Patent Application Nos. 2108390, 2122903 and 2166957 disclose vaporisers in which active substances capable of modifying the local atmosphere e.g. insecticides, deodorants and aromatics are vaporised for dispersion to the atmosphere. The active substance is carried or impregnated on a belt or tape consisting of a suitable base material, in such a state that vaporisation can be conducted at ambient temperature or under administration of localised heating by a vaporising head. The substance is maintained in an inactive condition until the belt passes over the vaporising head whereby thermal release is achieved. The belt may be moved to the vaporising head by hand or at a fixed speed by a motor driving feed means through a reduction gear and is taken up by a shaft or spindle. In one embodiment the belt is contained in a cassette to provide a re-usable device, the cassette being engaged by drive means and having a suitable aperture for the belt to pass across the vaporising head. None of the vaporisers disclosed are designed or suitable for delivering a predetermined unit dose of powdered solid medicament to a patient.
It has now been found that predetermined doses of a dry powder may be stored in and dispensed from a sheet material having drug-filled depressions in the surface thereof.